1. Field of the Invention
The present invention is directed to a folding stage, and in particular, to a stage having an adjustable spacing linkage for locking and adjusting the position and alignment of the stage decks.
2. Prior Art
Folding stages are used for a variety of purposes to provide a temporary raised platform for use in schools, hotels, convention centers and other institutions or multiple use facilities requiring the capability of setting up temporary stages. Such stages may be positioned adjacent one another to form a stage surface or positioned to support bridging decks between the stages to form an extended stage surface. When not in use, the stages have a framework that folds to compact dimensions for better storage. Stages typically have two stage decks hinged together along a center line to provide folding action with legs that remain substantially vertical when the stage decks fold. An example of such a folding stage is shown in U.S. Pat. No. 5,325,640 to Luedke et al., issued Jul. 5, 1994, and assigned to Sico, Incorporated, the Assignee of the present invention. Although the Luedke et al. patent shows a useful and efficient folding stage, further improvements are still possible, particularly with locking and aligning folding stages.
A common problem that occurs with folding stages and that generally increases over time, is the adjustment of the stage to ensure that the decks remain substantially aligned and horizontal in the unfolded use position. Prior stages typically utilize a bolt at the center line of the stage that acts as a stop where the two deck frameworks come together along the folding center line. Adjustment of the stop adjusts the relative position of the frame and the decks. These types of stages also use a spacing linkage to apply tension to the stage in the use position to prevent accidental folding and to take up any looseness that would allow the stage to wobble or shift. As this linkage passes through a toggle position to a locked position, the decks are pulled to a slightly concave alignment before they revert back to level. At this point, the leveling bolt acts as a spring with an extremely high spring constant that must be compressed before it can return to the level position. Although this configuration prevents folding and does provide some alignment, it does not always provide adequate compression, forcing other portions of the linkage to have some play in order to allow the linkage to pass through the toggle position. Over time, the components may wear and/or loosen, changing alignment so that the bracing of the framework is less rigid and has even more play. This condition results in a stage feeling less stable in the unfolded use position.
A spacing linkage includes a stop to lock the stage at a desired use position. If the spacing linkage can be adjusted, the alignment of the decks may be maintained or realigned by changing the final stop position of the spacing linkage. As the final resting position of the spacing linkage is slightly below horizontal after passing through a toggle position so that the spacing linkage snaps into a locked position, the various links in the linkage and the relative positioning points provide choices for adjustment. As shown in FIG. 1, the vertical distance below horizontal may be adjusted or the length of the pivot links may be changed. The horizontal distance is generally fixed as the stage framework is typically fixed. As the three links form a right triangle and the length of the hypotenuse is governed by the formula: A.sup.2 plus B.sup.2 equals C.sup.2 where A is the horizontal distance between the center point and the outer pivot position of the spacing linkage; B is the vertical distance below the horizontal at the stop position; and C is the length of the link. The adjustment of the link C changes at least one of the other factors. Since B is substantially constant, a smaller change in C will result in a greater change in A, governed by the formula A equals the square root of (C.sup.2 -B.sup.2), wherein B.sup.2 is substantially constant. Therefore, a small adjustment in the distance of the link will provide a greater adjustment in the relative position of the vertical stop position of the spacing linkage and overall alignment of the stage. Although the relative vertical engagement for stopping the links may change the stop position, depending on the distance needed, an adjustable vertical member providing direct vertical adjustment at the center of the linkage may not be sufficient to correct misalignment in the stage.
It can be seen then that a new and improved folding stage is needed that overcomes the problems with the prior art. An improved folding stage should provide a locking and spacing mechanism that can be easily adjusted that does not cause the components to loosen and lead to wobbling and a less stable stage. The spacing linkage should provide sufficient adjustability to provide proper alignment of the stage decks in the use position. The present invention addresses these as well as other problems associated with spacing linkages.